alpha-Amylase adsorption on starch crystallites

The goal of this work was to characterize the adsorption of Bacillus subtills alpha-amylase onto crystalline starchy materials of the B-type polymorph. Monodisperse spherulitic particles (R z6; 5.0 mum), essentially resistant to alpha-amylolysis at 25 degrees C were prepared from short amylose chains (DP(n) approximately 15). The alpha-amylase adsorbed specifically onto the spherulites, and adsorption was found to be a prerequisite step for hydrolysis. Adsorption was inhibited by the presence of maltose and maltotriose in the reaction mixture. Adsorption isotherm of the enzyme on the particles showed a well developed plateau of 1.62 mug/cm(2) at 25 degrees C corresponding to a monolayer adsorption process. The binding free energy calculated from the initial slope of the isotherm was DeltaG approximately -20.7 kJ/mol. This is smaller than published values for the binding of alpha-amylase to soluble amylosic chains (DeltaG < -30 kJ/mol).